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AVS 3011 – Eye Dissection – Special Senses

Key Concepts of Eye Dissection and Special Senses

  • Five Major External Special Senses

    • Vision
    • Audition (hearing)
    • Tactile (touch)
    • Gustation (taste)
    • Olfaction (smell)

  • Sensations

    • Result from stimuli leading to afferent impulses reaching the cerebral cortex.
    • Include somatic senses (pain, cold, heat, touch, pressure) and special senses.

  • Sensory Receptors

    • End organs of afferent nerves; responsible for converting stimuli into action potentials.
    • Main Groups:
    • Exteroceptors: Detect external stimuli (skin sensations, hearing, vision)
    • Interoceptors: Detect internal stimuli (taste, smell, responses to pH, distention)
    • Proprioceptors: Signal deep body conditions; located in skeletal muscles, tendons, ligaments, and joint capsules.

Structure and Function of the Eye

  • Receptor Organ for Vision:

    • Specific structures adapted for transparency allowing light rays to reach receptor cells.

  • Eye Structure:

    • Eyeball (globe)
    • Optic Nerve
    • Accessory Structures: Eyelids, conjunctivae, lacrimal apparatus, muscles.

Exterior Structures of the Eye

  • Fat

    • Purpose: Provides cushioning; loss of fat may cause sunken eyes in illness.

  • Muscles

    • Innervated by cranial nerves for eye movement.
    • Holds eyeball in its orbit against fat pad.

  • Optic Nerve

    • Bundle of nerve fibers transmitting visual information from retina to brain.

  • Conjunctiva

    • Membranes lining eyelids; forms a conjunctival sac for tears.
    • Normal color: pink; pale indicates anemia; blue for lack of oxygen.
    • Inflammation = conjunctivitis.

  • Tunics of the Eye

    1. Fibrous Tunic (outermost): Cornea and sclera.
    2. Vascular Tunic (Uvea): Choroid, ciliary body, iris.
    3. Nervous Tunic (innermost): Retina.
    • Retina contains photoreceptor cells converting light into electrical signals.

Key Eye Components

  • Sclera: Tough, white layer; site for muscle attachment.
  • Cornea: Transparent front portion covering iris and pupil; contributes to vision clarity.
  • Aqueous Humor: Fluid filling anterior chamber of the eye; increase leads to glaucoma.
  • Iris: Colored diaphragm; controls pupil size.
    • Muscles adjust pupil size in response to light.

Internal Structures of the Eye

  • Lens

    • Transparent, biconvex structure that focuses light onto the retina.
    • Suspensory ligaments attach lens to ciliary body.
    • Accommodates according to object distance.
    • Conditions affecting lens: Lenticular sclerosis (grey tint in aging) and Cataract (clouding).

  • Vitreous Body

    • Large cavity behind lens; helps maintain eye shape.

  • Retina

    • Contains rods (night vision) and cones (color vision).
    • Fovea Centralis: Area of highest visual acuity.

  • Choroid Layer

    • Pigmented, vascular layer preventing light reflection.

  • Accessory Structures

    • Lacrimal glands produce tears; keep eye moist and clean.
    • Meibomian glands help form a tear barrier.

Accommodation and Visual Response

  • Accommodation: Adjustment of lens shape to focus on objects at varying distances.

    • Relaxed lens: Flat for distant objects.
    • Contracted lens: More convex for near objects.

  • Pupil Response

    • Changes in size based on light exposure; different responses in light vs. dim conditions.

Experimentation

  • Accommodation Experiment: Visual focus shifting from near to far objects; observe lens status and response in ciliary muscles.
  • Vision Response Test: Observe pupil dilation in different lighting conditions; explain physiological responses.

Overall Anatomical Context

  • Optical Components:
    • Light passes through cornea, lens, and vitreous body before reaching retina.
    • Inverted image formed on the retina transmitted via optic nerve to the brain.

Vision Conditions

  • Emmetropia: Normal vision.
  • Hyperopia (Farsightedness): Difficulties focusing on near objects.
  • Myopia (Nearsightedness): Difficulties focusing on distant objects.
  • Field of Vision: Spatial perception affected by eye placement; overlapping fields enhance depth perception for predatory animals.

Dissection Protocol (Eye Dissection)

  1. Begin with cow eye; observe exterior structures.
  2. Remove cornea, lens, vitreous body; identify internal structures (aqueous humor, retina).
  3. Repeat with pig and sheep eye.
  4. Conduct experiments on accommodation and reflex responses.